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360 Lose timing belt.

Discussion in '360/430' started by tonino ct, Feb 23, 2021 at 7:24 PM.

  1. tonino ct

    tonino ct Karting

    Mar 1, 2018
    87
    Full Name:
    tonino tony
    Hi guys. I need an opinion. I removed the timing belts covers and i noticed the left belt was completely lose. The hydraulic tensioner is basically down to zero. I tried to lose the 17m on the bearing nut and the hydraulic tensioner came out and i was able to insert the pin. My question is :what causes this to happen and how can you tell id the Hydraulic tensioner is good? Also my belt was done from a professional 2 years ago about 5k miles ago along with the mejor service.
    i dont want to spent 500$ for the HT if i dont need it.
    any advice will help. thank you.
    tony.
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  3. fotostars

    fotostars Karting
    Silver Subscribed

    Feb 6, 2015
    245
    Bay Area
    Had the same "issue" when I opened the cover for the first time... A little "panic moment" but happy nothing got broken...

    Well, it turns out that it all depends where and how the motor stopped the last time it was run. You cannot check the tension of the belt at anywhere else than TDC on the compression stroke of Cyl #1. So turn the engine by hand clockwise using a 36 or 32mm (don't recall) on the main crankshaft pulley until you bring the engine to TDC and check the tension then.

    Now, it looks like you've already loosen the tensioner bearing so unfortunately you'll have to re-do the tension at TDC following the workshop manual procedure. PM me if you need a link to download it.
     
  4. tonino ct

    tonino ct Karting

    Mar 1, 2018
    87
    Full Name:
    tonino tony
    Thanks for the tips. Now i need to buy the tensioner tool. I should have waited for the responce.
     
  5. tonino ct

    tonino ct Karting

    Mar 1, 2018
    87
    Full Name:
    tonino tony
    Please send the link. Thanks.
     
  6. FiatAbarth850

    FiatAbarth850 Karting

    Aug 2, 2020
    63
    Winnipeg, Manitoba, Canada
    Full Name:
    Bill H.
    Can you explain why? Are you saying that the cam belt tension changes according to the position of the crankshaft? How does it do that?
     
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  8. tonino ct

    tonino ct Karting

    Mar 1, 2018
    87
    Full Name:
    tonino tony
    My meccanic said the same thing. Spin the motor over and let it settle for a few minute & see how the tension is.Thats what he wrote me back. But i was to late. I already loosened the tensioner
     
  9. eric355

    eric355 Formula Junior
    Silver Subscribed

    Nov 30, 2005
    977
    Toulouse (France)
    Full Name:
    Eric DECOUX
    It's all due to where the cams stop in their cycle.
    Depending on the stop position, the valve springs create a torque on each cam in one direction or the other. That results in variable tensions in the 3 strands of the belt.
    Belt tension must always be checked at the same position and Ferrari selected the #1 TDC.
     
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  10. mike32

    mike32 F1 Rookie

    May 13, 2016
    3,183
    Uk
    My old mondial, you could check the tension by finding the longest run and when you could twist it by 45 deg in the middle of the long run , then it was right. Lot to be said for the simple old engines
     
  11. fotostars

    fotostars Karting
    Silver Subscribed

    Feb 6, 2015
    245
    Bay Area
    Check your PM...
     
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  13. FiatAbarth850

    FiatAbarth850 Karting

    Aug 2, 2020
    63
    Winnipeg, Manitoba, Canada
    Full Name:
    Bill H.
    Hmmm. I could see that if there was only one set of cam lobes involved but with cam lobes pointing every which way down the length of the camshafts it doesn't seem to make sense to me. But, if it says that is the WSM then it must be so!
     
  14. eric355

    eric355 Formula Junior
    Silver Subscribed

    Nov 30, 2005
    977
    Toulouse (France)
    Full Name:
    Eric DECOUX
    On our V8, the cam lobes are 90° apart on each camshaft. If you try to turn such a camshaft by hand (no belt), you will find that it can stay fix (no torque due to valve springs) only at some stable and unstable positions. Stable positions are where 2 cam lobes are compensating each other, unstable is when 1 cam lobe is at max opening with almost no effect of other cams.
    In between these stable positions (where the camshaft has no effect on belt tension) the torque resulting of all the valve springs and cam lobes can be in one direction or the other. If the engine stop there (between stable positions) this torque will have a direct impact on the tension of the 2 strands of the belt connected to the pulley.
     
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  15. 360+Volt=Prius

    360+Volt=Prius Formula 3
    Silver Subscribed

    Sep 1, 2013
    1,377
    Western Mass
    Full Name:
    Raimondo
    I totally agree with eric355. I can say from experience if a particular lifter is on the high portion of the slope of a cam lobe it is pre-loaded by the valve spring, and can cause the cam to rotate. In This case would be toward the leading edge of the cam pulley because it can cause slack on that portion of the belt that is normally tight when engine is spinning forward. That would be sort of the equivalent of spinning the motor backwards even if the crank didn’t move.

    Cam rotation happened to me when I was degreeing my engine. Had the cam pulley bolts loose and cam slipped due to that preload from the valve spring on a cam lobe. My Heart skipped a beat when cam slipped.


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